U.S. Pat. No. 7,234,487 describes a hydraulic valve that is used with a hydraulic circuit, which includes a first oil channel and a second oil channel. The hydraulic valve discharges oil out of the first oil channel to the second oil channel when the hydraulic pressure of the first oil channel exceeds a predetermined value and out of the second oil channel to the first oil channel when the hydraulic pressure of the second oil channel exceeds a predetermined valve. In this manner, the hydraulic valve adjusts the hydraulic pressure of each of the first oil channel and the second oil channel to the predetermined valve or below.
As shown in FIG. 8, a conventional hydraulic valve 200 includes a housing 210 that includes a first port 211, which is connected to a first oil channel, and a second port 212, which is connected to a second oil channel. The housing 210 includes an inward projection between the first port 211 and the second port 212. The projection includes a corner portion, which defines a valve seat 213.
A poppet valve 220, which fluidically blocks the first oil channel and the second oil channel, is elastically pressed against the valve seat 213 by a compressed coil spring 230. The poppet valve 220 includes an intermediate portion the diameter of which decreases as extending away from the spring 230, defining a first taper 221, and a distal portion the diameter of which decreases toward the distal surface of the poppet valve 220, defining a second taper 222. When the second taper 222 contacts the valve seat 213, the first port 211 and the second port 212 are fluidically blocked.
When the hydraulic pressure of the first oil channel exceeds a predetermined value, the hydraulic pressure of the first port 211 presses the distal portion of the poppet valve 220. This separates the second taper 222 from the valve seat 213 against biasing force of the spring 230. Consequently, the first port 211 and the second port 212 come into fluidal communication, and oil flows from the first port 211 to the second port 212. On the other hand, when the hydraulic pressure of the second oil channel exceeds a predetermined value, the hydraulic pressure of the second port 212 presses the first taper 221 and the second taper 222 is separated from the valve seat 213 against the biasing force of the spring 230. Consequently, the second port 212 and the first port 211 come into fluidal communication, and the oil flows from the second port 212 to the first port 211.